An electromagnetic actuator for operating a cylinder valve in a piston-type internal-combustion engine essentially comprises two spaced electromagnets, whose pole faces are oriented toward one another. An armature connected to the cylinder valve to be actuated is guided back and forth between the pole faces against the force of restoring springs. When the armature is at rest, it is located in its center position between the two pole faces. As the two electromagnets are alternatingly energized, the armature arrives into contact with the pole face of the momentarily energized (capturing) electromagnet against the force of a restoring spring. If the holding current force of the restoring spring accelerates the armature in the direction of the other electromagnet which is energized with a capturing current during the armature movement. As a result, after overshooting the center position, the armature arrives into contact with the other, capturing electromagnet against the force of the restoring spring associated with the last-mentioned electromagnet. One of the electromagnets serves as a closing magnet holding the cylinder valve in a closed position against the force of the opening spring (that is, one of the restoring springs), while the other electromagnet serves as an opening magnet holding the cylinder valve in an open position against the force of the associated closing spring (that is, the other restoring spring).
To start an electromagnetic actuator of the above-described type, the two electromagnets are alternatingly supplied with current at the known resonant frequency of the spring-mass system which is composed of the restoring springs, the armature and the cylinder valve. The current supply at the resonant frequency is effected until the armature comes to rest at one of the electromagnets. By means of suitable data inputted in an engine control unit (ECU) which controls the energization of the two electromagnets, the oscillation-startup process may be terminated in such a manner that the armature comes to rest at a predetermined electromagnet, typically the closing magnet. In a multi-cylinder piston-type internal-combustion engine, the cylinder valves of the individual cylinder, or groups of cylinders, are brought into the closed position in this way by the oscillation startup, so that the individual cylinder valves can be actuated from the closed position to start the engine in the predetermined ignition- and work-cycle sequence.
To regulate the current supply, a sensor assembly responds as the armature approaches the capturing electromagnet, particularly to reduce the capturing current shortly before the armature impacts on the pole face of the capturing electromagnet. For this purpose a control signal may be emitted when the armature reaches a predetermined position relative to the pole face, or the traveled path is detected or, by derivation, the speed is determined or the speed is directly sensed. These approach-dependent values can be utilized by the engine control unit to reduce the capturing current such that the armature impacts the pole face gently, that is, with a speed slightly above "zero". As a result, the respective electromagnet has to be supplied only with a low holding current.
The above-outlined normal oscillation-startup method and normal operation, however, cannot be performed if at the engine, and particularly at the electromagnetic actuator, a low temperature level prevails. Such a low temperature, for example, appreciably increases the viscosity of the lubricating oil and/or changes the fit and thus increases the friction between the moving parts of the spring-mass system due to the heat-caused expansion of materials. A low temperature level in terms of the invention would be, for example, 0.degree. C.